1. Field of the Invention
The invention generally relates to an apparatus for adaptive signal processing and, in particular, an adaptive processor including beamforming and null-steering for an array antenna.
2. Description of the Prior Art
Phase-coded spread spectrum communication signals may be acquired and synchronized in the presence of interference with the aid of an adaptive array antenna under the control of a well-known LMS (least mean square) algorithm performing power minimization. However, the signal to interference (S/I) ratio at the adaptive array output port of a system using this type of processing, although adequate for acquisition and synchronization, provides undesirable message quality which, at best, is several decibels below the theoretical maximum obtainable when direction of arrival (beam steering) information is available.
In narrow band interference (e.g., AM radios) communication systems, the spectral bandwidth of the interference source is significantly wider than the desired signal's bandwidth. Null-steering in such a case may be obtained by an LMS algorithm with spectral preconditioning of control signals of an adaptive processor to prevent null formation on the desired signal.